Radio frequency communication

ABSTRACT

An analog modem circuit and carrier recovery method are disclosed for use between an RF receiver and a digital modem circuit configured for receiving a baseband RF input signal, and including an up-converter with frequency supplied by an up-converter voltage controlled oscillator, VCO; a down-converter with frequency supplied by a down-converter VCO; a Costas loop sub-module; and baseband outputs from the down-converter to a digital modem circuit. The up-converter feeds the down-converter, and the Costas loop module performs Costas loop functionality on the output of the down-converter to control the up-converter VCO frequency output to thereby control modification of rotation of symbols of the baseband signal.

FIELD OF THE INVENTION

The present invention relates to radio frequency (RF) communication. Thepresent invention also relates to an analogue modem circuit for usebetween an RF receiver and a digital modem circuit. The presentinvention also relates to a carrier recovery method.

BACKGROUND

Radio frequency (RF) communication, including point-to-point RFcommunication, is well known.

For outside broadcasting applications, there are many scenarios wheremultiple communication units, each coupled to a respective televisioncamera, are required to transmit video data to a central productioncommunication unit (and sometimes operate bi-directionally, i.e. alsoreceive video data transmitted by the central production communicationunit).

It is known that transmissions in a frequency band of 57 to 64 GHzlocated around 60 GHz undergo strong atmospheric absorption, and that inthe UK and other countries these frequencies form an “unlicensed band”.The equipment however has to conform to the relevant regulatorytechnical specifications to ensure that interference is not provided tothose operating within adjacent licensed bands. This frequency band isalso potentially attractive for point-to-point communication due to thestrong atmospheric absorption limiting interference from other signals.However, such characteristics also would conventionally lead todifficulties in achieving desired transmission distances for e.g.outside broadcast applications, especially if modulation, transmissionand reception apparatus is desired to be relatively small in size forreasons of portability and so on. This difficulty is exacerbated byincreasing video data rates, e.g. if it were desired to performpoint-to-point transmission of uncompressed High Definition (HD) SerialDigital Interface (SDI) video signals (1.485 gigabits/second).

For example, conventional transmitter modules and receiver modules forinterfacing transmitter and receiver integrated circuits (i.e. chips)and other elements, using discrete waveguide connections and the like,with commensurate stringent electromagnetic separation requirements at60 GHz, tend to be bulky and cumbersome.

Also, with regard to achieving relatively long range performance(e.g. >1 km), conventional analogue modem designs typically limitperformance when operating in a channel suffering from fading. An alldigital modem solution may offer better performance but would have anumber of disadvantages in terms of size, weight, power consumption andcost.

SUMMARY OF THE INVENTION

In a first aspect, the present invention provides an analogue modemcircuit for use between a radio frequency, RF, receiver and a digitalmodem circuit; the analogue modem circuit comprising: inputs forreceiving a baseband RF input signal from an RF receiver; anup-converter with frequency supplied by an up-converter voltagecontrolled oscillator, VCO; a down-converter with frequency supplied bya down-converter VCO; a Costas loop sub-module; and outputs foroutputting baseband outputs from the down-converter to a digital modemcircuit; wherein: the up-converter feeds the down-converter, and theCostas loop module performs Costas loop functionality on the output ofthe down-converter to control the up-converter VCO frequency output tothereby control modification of the rotation of the symbols of thebaseband signal as it is up-converted and then down-converted to providethe baseband outputs.

At least one of the VCOs may be controlled dependent upon a residualfrequency difference between the two VCOs at the output from thedown-converter, at a time when the Costas loop functionality is beingstarted.

The controlling may be performed at a first lock-in attempt of theCostas loop functionality.

The controlling may be performed at a recalibration stage of the Costasloop functionality.

The residual frequency difference may be determined when holding thebaseband inputs at fixed levels, representing a fixed symbol.

The analogue modem circuit may further comprise a complex basebandfilter with a constant frequency-amplitude slope, wherein the residualfrequency is determined by comparing signal levels before and after thefilter.

In a further aspect, the present invention provides a carrier recoverymethod performed by an analogue modem circuit for use between a radiofrequency, RF, receiver and a digital modem circuit; the methodcomprising: receiving a baseband RF input signal from an RF receiver atinputs of the analogue modem circuit; an up-converter voltage controlledoscillator, VCO, supplying a frequency to an up-converter; adown-converter VCO supplying a frequency to a down-converter; theup-converter feeding the down-converter; a Costas loop module performingCostas loop functionality on the output of the down-converter to controlthe up-converter VCO frequency output to thereby control modification ofthe rotation of the symbols of the baseband signal as it is up-convertedand then down-converted to provide baseband outputs; and outputs of theanalogue modem circuit outputting the baseband outputs.

At least one of the VCOs may be controlled dependent upon a residualfrequency difference between the two VCOs at the output from thedown-converter, at a time when the Costas loop functionality is beingstarted.

The controlling may be performed at a first lock-in attempt of theCostas loop functionality.

The controlling may be performed at a recalibration stage of the Costasloop functionality.

The residual frequency difference may be determined when holding thebaseband inputs at fixed levels, representing a fixed symbol.

The residual frequency difference may be determined by comparing signallevels before and after a complex baseband filter.

In a further aspect, the present invention provides one or moreprocessors arranged to operate in accordance with the method of any ofthe above or below aspects.

In a further aspect, the present invention provides an analogue modemcircuit and carrier recovery method for use between an RF receiver and adigital modem circuit; comprising: receiving a baseband RF input signal;an up-converter with frequency supplied by an up-converter voltagecontrolled oscillator, VCO; a down-converter with frequency supplied bya down-converter VCO; a Costas loop sub-module; and outputting basebandoutputs from the down-converter to a digital modem circuit; wherein: theup-converter feeds the down-converter, and the Costas loop moduleperforms Costas loop functionality on the output of the down-converterto control the up-converter VCO frequency output to thereby controlmodification of the rotation of the symbols of the baseband signal.

One or both VCOs may be controlled dependent upon a residual frequencydifference between the VCOs when the Costas loop functionality is beingstarted.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration (not to scale) of an example outsidebroadcast scenario in which a wireless communication system may be used;

FIG. 2 is a schematic block diagram of certain details of a cameracommunication unit of the wireless communication system of FIG. 1;

FIG. 3 is a simplified schematic illustration (not to scale) of the mainphysical constructional details of the camera communication unit of FIG.2;

FIG. 4 is a simplified exploded-view schematic illustration (not toscale) showing further details of certain constituent parts of atransceiver of the camera communication unit of FIG. 2;

FIG. 5 is a simplified schematic illustration (not to scale) showingfurther details of an example length (in cross-section) of an RF boardof the camera communication unit of FIG. 2;

FIG. 6A is a perspective view of a diplexer of the camera communicationunit of FIG. 2;

FIG. 6B shows (schematically and not to scale) a cross-sectional view ofthe internal features of the diplexer of FIG. 6A;

FIG. 7 is a schematic (not to scale) illustration of a top plan view ofa receiver transition arrangement;

FIG. 8 is a schematic (not to scale) perspective illustration of certainelements of the receiver transition arrangement of FIG. 7;

FIG. 9 is a further schematic (not to scale) cross-sectional view of theRF board of the camera communication unit of FIG. 2;

FIG. 10 is a schematic (not to scale) illustration of a top plan view ofa receiver transition arrangement;

FIGS. 11A and 11B are schematic (not to scale) illustrations of a topplan view of a differential transmitter RF coupling element (which mayalso be called an RF probe element) transition arrangement; and

FIG. 12 is a circuit diagram showing certain elements of a receive modemanalogue circuit of the camera communication unit of FIG. 2.

DETAILED DESCRIPTION

FIG. 1 is a schematic illustration (not to scale) of an example outsidebroadcast scenario in which a first embodiment of a wirelesscommunication system 1 may be used. In this scenario, the outsidebroadcast is of a motor sport race held over a racetrack 2. The wirelesscommunication system 1 comprises a plurality of television cameras 4.Each television camera 4 comprises, in addition to video camerafunctionality, a respective display 5. Each television camera 4 anddisplay 5 is coupled to a respective camera wireless communication unit6. (In other embodiments, for some or all of the television camera4—camera communication unit 6 pairs, the display 5 may be separate fromthe television camera 4 and instead coupled directly to the cameracommunication unit 6. In other embodiments, some or all of the of thetelevision camera 4—camera communication unit 6 pairs may not include orbe coupled to a display for displaying received video signals, even ifthe camera communication unit 6 is capable of receiving and processingsuch signals).

The communication system 1 further comprises a production wirelesscommunication unit 8. The production communication unit 6 is coupled toa broadcast unit 10. The broadcast unit 10 comprises, in addition tobroadcast functionality, a display 5. The camera communication units 6each comprise a respective antenna 12, and in this embodiment theproduction communication unit 8 comprises a plurality of antennas 12. Inthis embodiment the production communication unit 8 is mounted in avehicle and its antennas 12 are mounted on an extending hoist part ofthe vehicle and the broadcast unit 10 is also mounted in a vehicle.

In operation, video signals (in this example pictures and sound)captured by each television camera 4 are transmitted from its respectivecamera communication unit 6 via its antenna 12, at frequencies in theregion of 60 GHz, in this example at uncompressed HD video data rates(1.485 gigabits/second), and received by the production communicationunit 8 via a respective antenna 12 for each transmitting cameracommunication unit 6. The production communication unit 8 forwards thesignals via (in this embodiment) a wired or optical fibre link to thebroadcast unit 10. The broadcast unit 10 processes the signals, and/orrecords the signals, and/or transmits the signals (or processed versionsthereof) onwards to a further destination entity, for example a maintelevision studio using, for example, a satellite antenna 14 or opticalfibre cable.

In this embodiment, the communication system 1 is bidirectional, i.e. inaddition to the above described operation, the production communicationunit 8 may transmit video signals via its antenna 12 which are receivedby the camera communication units 6 via their respective antennas 12, atfrequencies in the region of 60 GHz, and in this example using standarddefinition (SD) SDI video data rates (270 megabits/second). Imagesdefined by such video signals may be displayed by the respective display5.

In this embodiment, the communication system 1 is able to achieve suchbidirectional high data rate communication over relatively largedistances between each camera communication unit 6 and the productioncommunication unit 8, thereby satisfying the requirement for a largearea event such as a motorsport race. For example, in this embodiment adistance between camera communication unit 6 and productioncommunication unit 8 of 1 km is readily accommodated.

FIG. 2 is a schematic block diagram of certain details of a cameracommunication unit 6 of the communication system 1. It is noted thatFIG. 2 and the description thereof is equally applicable to theproduction communication unit 8, except where stated otherwise.

The camera communication unit 6 comprises a video input 120, a videooutput 220, a transmit modem 23, a receive modem 25, a radio frequencytransceiver 26 for operation in a frequency band extending around 60GHz, and the above mentioned antenna 12.

The transmit modem 23 comprises a transmit modem digital circuit 122 anda transmit modem analogue circuit 124. The receive modem 25 comprises areceive modem digital circuit 222 and a receive modem analogue circuit224. The transceiver 26 comprises a transmitter circuit 126, a receivercircuit 226, and a diplexer 34.

In this embodiment, at least the majority of the components of bothmodem digital circuits, i.e. the transmit modem digital circuit 122 andthe receive modem digital circuit 222, are mounted on a single circuitboard, namely a digital modem board 22 (shown in FIG. 3). Also, in thisembodiment, at least the majority of the components of both modemanalogue circuits, i.e. the transmit modem analogue circuit 124 and thereceive modem analogue circuit 224, are mounted on a further singlecircuit board, namely an analogue modem board 24 (shown in FIG. 3). Thetransmit modem 23, the receive modem 25, and the transceiver 26 arephysically mounted in an enclosure 28, and the antenna 12 iselectrically coupled to the transceiver 26 and physically mounted on theenclosure 28.

The video input 120 is for coupling to the television camera 4. Thevideo input 120 is further coupled to the transmit modem digital circuit122. The transmit modem digital circuit 122 is further coupled to thetransmit modem analogue circuit 124. The transmit modem analogue circuit124 is further coupled to the transmitter circuit 126. The transmittercircuit 126 is further coupled to the diplexer 34. The diplexer 34 isfurther coupled to the antenna 12.

The video output 220 is for coupling to the display 5. The video output220 is further coupled to the receive modem digital circuit 222. Thereceive modem digital circuit 222 is further coupled to the receivemodem analogue circuit 224. The receive modem analogue circuit 224 isfurther coupled to the receiver circuit 226. The receiver circuit 226 isfurther coupled to the diplexer 34. A mentioned in the precedingparagraph, the diplexer 34 is further coupled to the antenna 12.

In overview, in the transmission part of the operation of the cameracommunication unit 6, an SDI digital video signal from the televisioncamera 4 is input via the video input 120 to the transmit modem digitalcircuit 122. The transmit modem digital circuit 122 performs errorcorrection coding and framing of the input SDI video signal suitable forthe modulation that is to follow in the transmit modem analogue circuit124, and passes the resulting processed signal to the transmit modemanalogue circuit 124. The transmit modem analogue circuit 124 modulatesthe digital signal to produce an analogue baseband differential in-phase(I) and differential quadrature (Q) Quadrature Phase Shift Keying (QPSK)signal in a form suitable for the transmitter circuit 126, and passesthe resulting analogue baseband I and Q signals to the transmittercircuit 126. The transmitter circuit 126 converts the analogue I and Qsignals to an approximately 60 GHz RF signal and transmits this signalvia the diplexer 34 and antenna 12 (to the production communication unit8 via a free space link).

Again in overview, in the reverse sense, i.e. in the reception part ofthe operation of the camera communication unit 6, an approximately 60GHz RF signal transmitted by the production communication unit 8 isreceived by the receiver circuit 226 via the antenna 12 and diplexer 34.The receiver circuit 226 converts the approximately 60 GHz RF signal toanalogue differential baseband I and Q signals, and passes this basebandsignal to the receive modem analogue circuit 224. The receive modemanalogue circuit 224 converts that signal to a form suitable for thereceive modem digital circuit 222 to operate on, and passes theresulting modulated analogue signal to the receive modem digital circuit222. The receive modem digital circuit 222 processes that signal to adigital form suitable for display (for example to display to an operatorof the television camera 4 the video image currently being selected forbroadcast transmission to the public), and passes the resulting digitalsignal to the video display 5 that in this embodiment is comprised bythe television camera 4.

In the case of the production communication unit 8 (as opposed to thecamera communication units 6), the video input 120 and video output 220are connected to the broadcast unit 10 and its display 5 rather than toone of the television cameras 4.

FIG. 3 is a simplified schematic illustration (not to scale) of the mainphysical constructional details of the camera communication unit 6 ofthis embodiment. As mentioned above, at least the majority of thecircuitry for both the transmit modem digital circuit 122 and thereceive modem digital circuit 222 is provided on a common given singleboard 22, namely the digital modem board 22. Also as mentioned above, atleast a majority of the circuitry for both the transmit modem analoguecircuit 124 and the receive modem analogue circuit 224 is provided on afurther common given board 24, namely the analogue modem board 24. Thetransceiver 26 is implemented in the form of a laminated structurecomprising an RF board 32 (on which are mounted at least the majority ofthe components forming the transmitter circuit 126 and the receivercircuit 226) and the diplexer 34 (a diplexer being a passive device thatprovides frequency domain multiplexing/de-multiplexing functions). Inthis embodiment the diplexer 34 is formed from, and has the outerdimensions of, a rectangular shaped solid block or slab. In thisembodiment the slab, i.e. the diplexer 34, is made of aluminium finishedwith an Iridite (trademark) surface finish. The laminated structure isprovided by the RF board 32 being bonded in laminated fashion to asurface of the diplexer 34. For convenience (i.e. this is not limiting),this surface is hereinafter referred to as the “inner diplexer surface36” (i.e. the term “inner” being in terms of the construction of thecamera communication unit 6). In this embodiment the cameracommunication unit 6 further comprises a separate power supply board 40that provides power for each of the digital modem 22, the analogue modem24 and the RF board 32.

The surface 38 of the diplexer 34 that is opposite the inner diplexersurface 36 is hereinafter referred to as the “outer diplexer surface38”. The diplexer 34 further comprises a common port 42 provided at theouter diplexer surface 38. The common port 42 comprises fixing means anda common port waveguide opening 43. The common port waveguide opening 43is an opening to a waveguide structure within the diplexer 34, whichwaveguide structure will be described later below.

The antenna 12 (for clarity not shown in FIG. 3) is mounted in proximityto the outer diplexer surface 38 and aligned with the common port 42such that in operation the antenna 12 is coupled to the common portwaveguide opening 43. In this embodiment the antenna 12 is a dielectricloaded horn antenna of diameter 250 mm and length 400 mm. However, thisneed not be the case, and in other embodiments other types of antennaand/or other sizes of antenna may be used. For example, a more compactantenna may be provided in the form of a twist reflect or transreflectantenna.

In this embodiment, the following items are held in a stacked, spacedapart arrangement in the enclosure 28 in the following order (withappropriate interconnections (not shown) provided between thesedifferent elements): the power supply board 40—the digital modem (board)22—the analogue modem (board) 24—the transceiver (laminated structure)26. The antenna 12 is mounted on the outside of the enclosure 28 withcoupling to the common port 42 arranged as described above. In thisembodiment the physical sizes of the various elements are such that, asindicated in FIG. 3, each of these elements has a surface area of widthapproximately 120 mm and height approximately 80 mm, with the stackedelements providing an overall depth when stacked (including gaps betweenthe elements) of approximately 75 mm. The 75 mm total depth is made upapproximately of the following individual thicknesses/gaps: diplexer34=10 mm, RF board 32=10 mm, gap=5 mm, analogue modem 24=10 mm, gap=5mm, digital modem 22=10 mm, gap=5 mm, power supply board 40=20 mm.Accordingly, the enclosure 28 need only be of approximate size 160mm×120 mm×80 mm.

FIG. 4 is a simplified exploded-view schematic illustration (not toscale) showing further details of certain constituent parts of the RFtransceiver 26 of this embodiment, and representing schematically theorder in which the various elements are assembled (this aspect will besummarised at the end of the description of FIG. 4). The same referencenumerals are used to indicate the same components where these have beenmentioned previously above.

In addition to the earlier described common port 42 on the outerdiplexer surface 38, the diplexer 34 further comprises two ports on theinner diplexer surface 36, namely (for ease of reference—either port mayin fact be used for either application) a transmitter port 44 and areceiver port 46. The transmitter port 44 comprises fixing means and atransmitter port waveguide opening 45. The transmitter port waveguideopening 45 is a further opening to the previously mentioned waveguidestructure that will be described later below. The receiver port 46comprises fixing means and a receiver port waveguide opening 47. Thereceiver port waveguide opening 47 is a further opening to thepreviously mentioned waveguide structure that will be described laterbelow.

The RF board 32 comprises a transmitter integrated circuit (IC) chip 50and a receiver IC 52 mounted directly on the surface 37 of RF board 32that faces away from the diplexer 34. The transmitter IC 50 and thereceiver IC 52 are mounted at positions that are approximately alignedwith the positions of the transmitter port 44 and the receiver port 46respectively. Wire or tape bonds are used to interconnect thetransmitter IC 50 and the receiver IC 52 with transmission lines etchedon the surface of the RF board 32. Additional supporting surface mount(SM) components are also mounted on the surface 37 of the RF board 32,these include: power supply regulators 302, crystal oscillators 304,digital serial control interface buffers 306, and multi-way interfaceconnectors 308. The components mounted on the RF board 32 provide, incombination, and where required with other conventional components, thetransmitter circuit 126 and the receiver circuit 226.

Two covers 60 (in this embodiment made of metal) are also positioned onthe surface 37 of the RF board 32. They are positioned over internalstructures within the RF board called transitions (not shown in FIG. 4)that will be described later below.

In other embodiments, instead of using a transmitter IC 50 and areceiver IC 52, the transmitter circuit 126 and the receiver circuit 226are implemented in the form of discrete components mounted on thesurface 37 of the RF board 32.

In this embodiment, the order in which the various elements describedabove are assembled is as follows. First, the diplexer 34 is provided.Then the bare form of the RF board 32 is bonded to the diplexer 34. Thenthe various components (other than the transmitter IC 50 and thereceiver IC 52) are mounted on to the surface 37 of the RF board 32.Then the transmitter IC 50 and the receiver IC 52 are mounted on to thesurface 37 of the RF board 32. Then the covers 60 are mounted on to thesurface 37 of the RF board 32.

FIG. 5 is a simplified schematic illustration (not to scale) showingfurther details of an example length (in cross-section) of the RF board32 of this embodiment. The same reference numerals are used to indicatethe same components where these have been mentioned previously above.

In this embodiment the RF board 32 comprises a laminated structure madeup of two double-sided copper clad printed circuit boards (pcb), namelyan “upper” (this term is used for convenience and is not limiting)double-sided pcb 62 and a “lower” (this term is used for convenience andis not limiting) double-sided pcb 64, with a bond ply adhesive layer 63positioned between the two double-sided pcbs 62, 64 which is used tobond together the two double-sided pcbs 62, 64. Each of the double-sidedpcbs 62, 64 comprises a 100 μm thick board structure made of liquidcrystal polymer (LCP) with 17 μm thick copper layers 68 on each of thetwo planar surfaces. The bond ply adhesive layer 63 comprises a 50 μmthick dielectric structure. Conducting vias (merely by way of examplecertain such vias 70, 70 a, 70 b are shown in FIG. 5) are providedbetween copper layers 68 as required to provide the requiredinterconnectivity. Some of the via structures are arranged as groundingposts by appropriately connecting/isolating them from one or more of thecopper layers 68. The vias 70 b are examples of these grounding posts.

Also shown in FIG. 5 is the receiver IC 52 bonded on the upper copperdouble-sided pcb 62. Wire or tape bonds 402 are used to interconnect theindividual connection pads on the receiver IC 52 to the copper track 68.One in particular is connected to the track connected to a via 70 a thatpasses to the opposing copper layer 68 of the upper double-sided pcb 62.At the via exit the via 70 a is connected to a track section of thecopper track 68. This track section is a continuous section of track,but for ease of explanation and in view of the two following portionsdifferent functionality, will be named or identified as a track section68 a that extends away from the via 70 a, and then an “RF probe element”track section 68 b that extends from the track section 68 a (note, theRF probe element track section may also be called an RF coupling elementtrack section). In other words, the track section 68 bprovides/functions as an RF probe element (which may also be called anRF coupling element). The RF probe element track section 68 b operateswith the coupling function of an RF probe element (here to couple thesignal from the relevant waveguide of the diplexer to the track section68 a and hence on to the receiver IC 52) by virtue of the followingisolation details and by virtue of being positioned (as described inmore detail below) in alignment with the waveguide opening so as tocouple with the waveguide opening. The copper tracks 68 on both sides ofthe lower double-sided pcb 64 are removed over an area of the lowerdouble-sided pcb 64 corresponding approximately to the area of thecorresponding waveguide, to thereby provide an area or region 72 of thelower double-sided pcb 64 where the lower double-sided pcb 64 acts as aninsulator. A corresponding arrangement (not shown) is provided for aconnection or connections (in the case of differential transmission)from the transmitter IC 50. These arrangements (be they reception ortransmission) may be termed transitions.

Also shown in FIG. 5 is one of the covers 60, mounted on the outersurface of the first double-sided pcb 62. The cover 60 is positioned inalignment with the above described transition, i.e. above the region 72and therefore also above the RF probe element track section 68 b, and isgrounded. The interior of the cover 60 thereby provides an air space atthe top of the transition arrangement. This air space is provided as aspecific distance between the RF probe element track section 68 b andthe cover 60 in terms of the wavelength of the approximately 60 GHzoperation (in this embodiment the distance is wavelength/4) to providepart of the transmitting or receiving functionality of the transition.

The RF board 32 is aligned with the diplexer 34 such that the RF probeelement track section 68 b is aligned with the receiver port waveguideopening 47 of the diplexer 34, so that in operation the receiver IC 52is coupled to the receiver port waveguide opening 47 (as described inmore detail below with reference to FIG. 7). Corresponding track sectionor sections (as described in more detail below, for example withreference to FIG. 11) is/are aligned with the transmitter port waveguideopening 45 of the diplexer 34, so that in operation the transmitter IC50 is coupled to the transmitter port waveguide opening 45.

FIGS. 6A and 6B are schematic illustrations (not to scale—indeed theaspect ratio is shown in a very distorted fashion to enable the variouselements to be seen clearly) showing certain further details of thediplexer 34, and in particular the waveguide structure mentionedpreviously above. The same reference numerals are used to indicate thesame components where these have been mentioned previously above.

FIG. 6A is a perspective view of the diplexer 34, showing for ease ofreference in one figure the following previously described elements: thecommon port waveguide opening 43 (at the outer diplexer surface 38), thetransmitter port waveguide opening 45 (at the inner diplexer surface36), and the receiver port waveguide opening 47 (also at the innerdiplexer surface 36). The transmitter port waveguide opening 45 and thereceiver port waveguide opening 47 are spaced apart from each other. Inthis embodiment, each of the waveguide openings 43, 45, 47 are locatedon the same centre line (in terms of the height of the diplexer 34) aseach other, more particularly they are located half-way up therespective diplexer surface 38, 36, at a height position indicatedschematically by the reference line “A-B” in FIG. 6A. However, this neednot be the case, and in other embodiments any one or more of theopenings may be at a different height position.

FIG. 6B shows (schematically and not to scale) a cross-sectional view ofthe internal features of the diplexer 34 in the plane defined by theline A-B.

The diplexer 34 comprises an air filled/hollow waveguide structuretherein, i.e. the waveguide structure is machined or otherwiseintegrated within the solid block that forms the diplexer 34. Thediplexer consists of three waveguide sections: a transmitter waveguide82, a receiver waveguide 84 and a waveguide combiner 80, that interfacewith the transmitter port waveguide opening 45, the receiver portwaveguide opening 47, and the common port waveguide opening 43respectively. This waveguide structure is the structure previouslymentioned in the description of FIGS. 3 and 4.

Apart from where they need to be shaped differently to merge etc., thetransmitter waveguide 82, the receiver waveguide 84, and the waveguidecombiner 80 each have rectangular cross-section and are configured toprovide openings/interfaces 45, 47 and 43 conforming to the waveguidestandard “WG25”. In consequence, the three waveguide openings 43, 45, 47are each of rectangular shape also. However it is not essential thatthis particular shape/size of waveguide is employed, and in otherembodiments other cross-sections, sizes and/or types may be employedinstead.

In this embodiment, the waveguide structure 80 is at the same height (interms of the height of the diplexer 34) as the waveguide openings 43,45, 47, i.e. is located half-way up the respective diplexer surface 38,36, at all of its extent across the diplexer 34. However, this need notbe the case, and in other embodiments its height may vary, i.e. it neednot remain fixed in any given plane.

In this embodiment, the transmitter waveguide 82, the receiver waveguide84 and the waveguide combiner 80 are machined to provide differentpassband frequency filter characteristics by machining such as toprovide filters 86 in the form of protrusions on the surfaces of thewaveguide walls. However, this is not essential, and in otherembodiments other ways or constructions for providing filtered operationmay be used instead.

In this embodiment, the transmitter waveguide 82 is tuned to a preferredfrequency passband of 57.895 GHz to 58.105 GHz and the receiverwaveguide 84 is tuned to a preferred frequency passband of 61.94 GHz to63.06 GHz. Alternatively these frequencies may be reversed, i.e. thereceiver tuned to 57.895 GHz to 58.105 GHz and the transmitter tuned to61.94 GHz to 63.06 GHz Moreover, these particular frequencies values arenot essential, and in other embodiments other frequencies in the regionof 60 GHz may be used instead.

In this embodiment the waveguide structure is formed in the solid blockof the diplexer 34 by machining the solid block to hollow out thewaveguide structure. The machining is controlled, or further machiningis performed, to provide the filters 86.

FIG. 7 is a schematic (not to scale) illustration of a top plan view ofa receiver transition arrangement 180. The receiver transitionarrangement 180 of FIG. 7 corresponds to various parts of the structuredescribed earlier, and in particular with the layout of various partsshown together also in FIG. 5. The same reference numerals are used toindicate the same components where these have been mentioned previouslyabove.

Certain of the elements providing the receiver transition arrangement180 are the following: the track section 68 a and its end section whichis the RF probe element track section 68 b, the receiver port waveguideopening 47, and the cover 60. (Also shown in FIG. 7 are the positions offixing screws 172 and location dowel pins 174 which are used forlocating and fixing the cover 60 to the RF board 32.) The RF probeelement track section 68 b is positioned such as to start at the alignedposition of the receiver port waveguide opening 47 at approximately themid-point of the longer side of the receiver port waveguide opening 47and then continue on so as to extend over approximately half the widthof the receiver port waveguide opening 47 where it ends in an opencircuited transmission line.

FIG. 8 is a schematic (not to scale) perspective illustration of certainelements of the receiver transition arrangement 180 described above withparticular reference to FIGS. 5 and 7. FIG. 8 is derived from a threedimensional electromagnetic model and shows a mixture of certainstructural details and certain modelling artefacts. The same referencenumerals are used to indicate the same components where these have beenmentioned previously above.

Accordingly, in FIG. 8 modelling x-y-z axes are shown for ease ofreference, and these are indicated by reference numerals 270 x, 270 yand 270 z. FIG. 8 further shows again the previously described tracksection 68 a and its end section which is the RF probe element tracksection 68 b. FIG. 8 also shows a plurality of grounding posts/groundedvias 70 b. Also shown in FIG. 8 is the modelling artefact of theairspace 272 provided between the cover 60 and the outer surface of theupper double-sided pcb 62. Similarly, also shown in FIG. 8 is themodelling artefact of the airspace 274 (which is provided by theinterior of the hollow receiver waveguide 84 shown previously in FIG.6).

Two reference lines, namely C-D and E-F are provided on FIG. 8 fordefining cross-sectional views that will be discussed below. The lineC-D passes through and extends along the same direction as the tracksection 68 a and RF probe element track section 68 b. The line E-Fextends in a direction parallel to line C-D, but passes through adifferent point of the Figure.

Referring back to FIG. 5, it can now be noted that FIG. 5 is a schematic(not to scale) cross-sectional view of the RF board 32 in the planedefined by the line C-D, although the range of the view in FIG. 5extends further to the left than that in FIG. 8.

FIG. 9 is a schematic (not to scale) cross-sectional view of the RFboard 32 in the plane defined by the line E-F. The same referencenumerals are used to indicate the same components where these have beenmentioned previously above.

It will be appreciated that the numbers of and positions of thegrounding posts/grounded vias 70 b in FIGS. 5, 8 and 9 are merelyschematic and by way of example only. These should in practice bepositioned and provided in appropriate quantities to provide appropriategrounding and prevention of parallel plate mode propagation.Conventional field mapping modelling tools may be used in the layoutdesign process.

FIG. 10 is a schematic (not to scale) illustration of a top plan view ofa receiver transition arrangement 180 used in a further embodiment. Thesame reference numerals are used to indicate the same components wherethese have been mentioned previously above. All details of thisembodiment are the same as those described above, including how thearrangement of FIG. 10 is implemented within the different layers of theRF board 32 and so on, except for a variation in the probe element tracksection 68 b as will now be explained in more detail.

In this further embodiment as shown in FIG. 10, the RF probe elementtrack section 68 b extends (again starting at approximately themid-point of the longer side of the receiver port waveguide opening 47)across the whole width of the receiver port waveguide opening 47 plus afurther short distance to form a shorted cross guide termination by thenconnecting to a grounded section of track (not shown). The length of thefurther short distance is accordingly one that provides the requiredtransmission line termination characteristics.

If desired, e.g. for reasons of simplicity, the transmitter transitionarrangement may be provided in corresponding detail to the abovedescribed possibilities for receiver transition arrangements. However,in this embodiment, the transmitter IC 50 uses a differential output andhence requires a different probe design than that described above forthe single ended receiver probe design.

FIGS. 11A and 11B are schematic (not to scale) illustrations of a topplan view of a differential transmitter RF coupling element (which mayalso be called RF probe element) transition arrangement 380 that may beused in versions where the transmitter IC 50 has a differential output.FIGS. 11A and 11B are two drawings of a differential transmitter RFcoupling element (RF probe element) transition arrangement 380, i.e.FIGS. 11A and 11B show the same arrangement as each other but havecertain parts labelled differently in the two figures for ease ofexplanation, as will be understood from the following description. Also,for clarity, in FIGS. 11A and 11B certain features are omitted comparedto those shown and labelled in corresponding FIGS. 7 and 10, and insteadin FIGS. 11A and 11B the view shown concentrates on the relevant coppertracks and the transmitter port waveguide opening 45.

As shown in FIGS. 11A and 11B, there are two substantially parallel(although it is not essential they are substantially parallel) coppertrack sections 368 a and 468 a that extend to a side of the transmitterport waveguide opening 45 (hereinafter referred to as the first side 445of the transmitter port waveguide opening). These copper track sections368 a, 468 a are the two differential equivalents to the single(non-differential) track section 68 a of the above described receivertransition arrangements.

As indicated by the reference numerals employed in the FIG. 11Arepresentation of the differential transmitter RF coupling element (RFprobe element) transition arrangement 380, the two copper tracks formingrespectively copper track sections 368 a, 468 a then each extend furtheras continuous tracks, although the further extending parts will bereferred to as specific sections of track, namely a first “RF couplingelement” (or “RF probe element”) track section 368 b (the extending partof the copper track section 368 a) and a second “RF coupling element”(or “RF probe element”) track section 468 b (the extending part of thecopper track section 468 a). Both the first RF coupling element tracksection 368 b and the second RF coupling element track section 468 bonly extend within the area of their respective port waveguide opening,i.e. they are “contained” within their respective waveguide aperturearea.

Further details of the two RF coupling element track sections 368 b, 468b are then shown by virtue of the reference numerals employed in theFIG. 11B representation of the differential transmitter RF couplingelement transition arrangement 380.

As shown in FIG. 11B, the first RF coupling element track section 368 bfunctionally comprises a first portion 368 c and a second portion 368 d.The first portion 368 c continues in the same direction as the tracksection 368 a that it is an extension of, so as to extend across thetransmitter port waveguide opening 45 to a point approximately half wayacross the transmitter port waveguide opening 45, thereby to a firstdegree of approximation functionally merely extending the transmissionline behaviour of the track section 368 a, since any coupling to thewaveguide is relatively weak. The second portion 368 d extends from thefirst portion 368 c, however the second portion 368 d extends in anangular direction to the direction that the track section 368 a andfirst portion 368 c extend along. This second portion 368 d will therebyperform the majority of the coupling from the track section 368 a to thewaveguide.

As also shown in FIG. 11B, the second RF coupling element track section468 b functionally comprises a first portion 468 c and a second portion468 d. The first portion 468 c continues in the same direction as thetrack section 468 a that it is an extension of, so as to extend acrossthe transmitter port waveguide opening 45 to a point approximately halfway across the transmitter port waveguide opening 45, thereby to a firstdegree of approximation functionally merely extending the transmissionline behaviour of the track section 468 a, since any coupling to thewaveguide is relatively weak. The second portion 468 d extends from thefirst portion 468 c, however the second portion 468 d extends in adifferent angular direction to the direction that the track section 468a and first portion 468 c extend along. This second portion 468 d willthereby perform the majority of the coupling from the track section 468a to the waveguide.

The angular direction of the second portion 468 d of the second RFcoupling element track section 468 b is opposed to the angular directionof the second portion 368 d of the first RF coupling element tracksection 368 b, i.e. in the case of the first RF coupling element tracksection 368 b, the second portion 368 d extends onward from the firstportion section 368 c away from the first side 445 of the transmitterport waveguide opening 45, whereas in the case of the second RF couplingelement track section 468 b, the second portion 468 d “turns back”toward the first side 445 of the transmitter port waveguide opening 45.

For comparison, it may be noted that if the second portions 368 d and468 d are omitted, the remaining first portions 368 c and 468 c wouldgenerate a higher order mode within the waveguide that would prove aless efficient coupling. This may be employed in alternativeembodiments.

However, in this embodiment, the inclusion also of the respective secondportions 368 d and 468 d with opposed angular directions in therespective RF coupling element track section 368 b and 468 b provides animproved coupling efficiency into the waveguide.

Moreover, this is particularly the case in the above embodiments inwhich the second portions 368 d and 468 d are provided in a buried layerwhich is an asymmetric buried layer. (Referring to FIG. 5, it is notedthat the buried layer is an asymmetric layer in the sense that due tothe constructional arrangement of the RF board 32, in particular theinclusion of the bond ply layer 63, the distance between the buriedcopper layer of the RF coupling element track sections 368 b and 468 band the copper layer at the outer surface of the upper double-sided pcb62 is different to the distance between the buried copper layers of theRF coupling element track sections 368 b and 468 b and the copper layerat the outer surface of the lower double-sided pcb 64.) The asymmetricalarrangement of the RF coupling element track sections 368 b and 468 band associated ground planes (in copper layer 68) is taken into accountduring the design of the track sections in order to provide the requiredtransmission line impedances.

In the differential transmission transition arrangement described withreference to FIGS. 11A and 11B, the second portions 368 d and 468 dfollow a straight direction, with a discrete angular interface(shape-wise) with respect to the first portions 368 c and 468 c.However, this need not be the case, and in other embodiments othershapes may be used for the second portions 368 d and 468 d, for examplecurved, with a gradual curved angular displacement from the respectivefirst portions 368 c and 468 c.

In the differential transmission transition arrangement described withreference to FIGS. 11A and 11B, the second portions 368 d and 468 d aresubstantially parallel with each other, i.e. their respective angleswith the first portions 368 c and 468 c are complementary to each other.However, this need not be the case, and in other embodiments they may beother than substantially parallel with each other.

The angular directions the second portions 368 d and 468 d make to thefirst portions 368 c and 468 c may be any angle, although angles of 30°to 60° or 120° to 150° are preferred, and angles substantially equal to45° and 125° are yet more preferred, as giving stronger effect (comparedto a conventional balanced transmission line arrangement), whereasangles that are close to 90° result in only a small level of effect(compared to a conventional balanced transmission line arrangement).

The copper track arrangements described above with reference to FIGS. 7,10 and 11 may conveniently be termed transition line interfaces (in thecase of FIG. 11, more particularly a differential transition lineinterface). Moreover, since they are provided in an inner layer of amultilayer RF board 32, they may more particularly be termed buriedtransition line interfaces, and in the case of FIG. 11 a burieddifferential transition line interface.

FIG. 12 is a circuit diagram showing certain elements of the receivemodem analogue circuit 224 of this embodiment.

The receive modem analogue circuit 224 comprises inputs 502 arranged toreceive baseband RF inputs from the receiver circuit 226. The receivemodem analogue circuit 224 further comprises low-pass filters 504, an IQmodulator (i.e. up-converter) 506, a band-pass filter 508, an IQdemodulator (i.e. down-converter) 510, a discriminator and controlfunction module 512 (the discriminator and control function module 512comprising a discriminator module 514 and a control function module516), a Costas loop sub-module 518, a down converter voltage controlledoscillator (VCO) 520, an up-converter VCO 522, and outputs 524 arrangedto output processed baseband outputs to the receive modem digitalcircuit 222.

The low-pass filters 504 are coupled to the baseband inputs 502 and theIQ modulator 506. In operation the low-pass filters 504 receive thebaseband RF inputs from the receiver circuit 226, perform low-passfiltering on them, and forward the low-pass filtered signals to the IQmodulator 506.

The IQ modulator 506 is further coupled to the up-converter VCO 522 andthe band-pass filter 508. In operation the IQ modulator 506 performsup-conversion on the signals making use of a frequency source providedby the up-converter VCO 522, and forwards the up-converted signals tothe band-pass filter 508.

The band-pass filter 508 is further coupled to the IQ demodulator 510.In operation the band-pass filter 508 band-pass filters the signals andforwards them to the IQ demodulator 510.

The IQ demodulator 510 is further coupled to the down-converter VCO 520,the discriminator module 514, the Costas loop sub-module 518, and thebaseband outputs 524. In operation, the IQ demodulator 510 performsdown-conversion on the signals making use of a frequency source providedby the down-converter VCO 520, and forwards the down-converted signalsto the discriminator module 514, the Costas loop sub-module 518, and thebaseband outputs 524.

The discriminator module 514 is further coupled to the control functionmodule 516. In operation the discriminator module performsdiscrimination on the signals and forwards a resulting output to thecontrol function module 516.

The control function module is further coupled to the down-converter VCO520. In operation, the control function module 516 performs a controlfunction based on the output received from the discriminator module 514and forwards a resulting control output to the down-converter VCO 520.

The Costas loop sub-module 518 is further coupled to the up-converterVCO 522. In operation, the Costas sloop sub-module 518 performs part ofthe role of a conventional Costas loop, and forwards a resulting controloutput to the up-converter VCO 522.

Making use of the control output received from the Costas loopsub-module 518, the up-converter VCO 522 determines the frequency valueto be employed as it acts, as mentioned above, as the frequency sourcefor the IQ modulator 506.

Making use of the control output received from the control functionmodule 516, the down-converter VCO 520 determines the frequency value tobe employed as it acts, as mentioned above, as the frequency source forthe IQ demodulator 510.

The baseband outputs 524 forward the down-converted signals receivedfrom the IQ demodulator 510 to the receive modem digital circuit 222.

In this embodiment, quadrature phase shift keying (QPSK) modulation isemployed, but other types of modulation may be employed instead, forexample quadrature amplitude modulation (QAM), minimum shift keying(MSK) and so on.

In overview, the receive modem analogue circuit 224 operates to removephase and frequency offsets that occur as part of thetransmission/modulation process. The resulting output is then a“stationary” constellation that can be readily decoded and furtherprocessed. That is, the modulation scheme (in this embodiment QPSK)applies rotation to the signals so that symbols of an incoming signalhave in effect “unknown phase” and, due to the offset frequency betweenthe two ends of the communications link not being known, also have a“spinning constellation”. The symbols are in effect “rotated” by thereceive modem analogue circuit 224 so that the modulation scheme (hereQPSK) constellation points are in effect “lined up” appropriately. Thatis the baseband signals output from the receive modem analogue circuit224 to the receive modem digital circuit 222 have had their frequencyand phase offsets removed (or at least reduced). This may generally beconsidered as a carrier recovery process. The extent of rotation isdetermined by the Costas loop sub-module 518. That is, the Costas loopsub-module 518 comprises those elements of a conventional Costas loopthat function to analyse the output being output by the receive modemanalogue circuit 224, determine how much rotation there is, and generatethe required signal for indicating what frequency is required forbalancing that rotation.

The extent of the rotation is then in effect controlled by the receivemodem analogue circuit 224 in a feedback manner by controlling thefrequency difference between the two VCOs 520, 522.

Further details of the above described operation of the receive modemanalogue circuit 224 are as follows.

The baseband inputs 502 from the receiver circuit 226 are converted toan intermediate frequency (IF) using the IQ modulator 506. Theup-converter VCO 522 that provides the frequency source for thisconversion is itself controlled by a loop that extracts the carrierphase from the symbol stream. This loop is based on a (conventional)Costas loop method. The IF is then filtered by the band-pass filter 508to remove any spurious signals and down-converted in the IQ demodulator510 using a second VCO, namely the down-converter VCO 520, as thefrequency source. When the carrier recovery loop is locked, the outputof the IQ demodulator 510 is rotated such that the receiver modulationconstellation is at the correct phase. These baseband signals can thenbe output to the receive modem digital circuit 222 for furtherprocessing. The carrier recovery loop recognises errors in the outputconstellation rotation and applies the appropriate corrections to theup-converter VCO 522.

The other VCO, i.e. the down-converter VCO 520, is controlled so thatthe nominal frequency of the two VCOs 520, 522 tracks long-term. Thediscriminator and control functions implemented by the discriminatormodule 514 and control function module 516 respectively are responsiblefor achieving this tracking. This ‘long-term’ tracking of the two VCOs520, 522 means that the carrier recovery loop does not need toaccommodate large frequency offsets which would otherwise lead todifficulty in acquiring and maintaining carrier lock. This tends togives rise to a straightforward, low power, low cost VCO design thatdoes not require onerous stability.

In the above operation, in effect the IQ modulator 506 converts theincoming low-pass filtered baseband input signals to an intermediatefrequency (IF).

Thus it will be appreciated by the skilled person that, in the receivemodem analogue circuit 224 as a whole, a portion of a conventionalCostas loop circuit has been used in combination with a differentapproach to up and down conversion than would normally be used in oreven considered for a conventional Costas loop. In other words, aconventional Costas loop would require a received signal being input tothe Costas loop to be in intermediate frequency form, having beenpre-processed in conventional form into that intermediate frequencyform. Therefore, if a skilled person desired to process an incomingbaseband signal using a conventional Costas loop, the obvious approachwould be to perform baseband to intermediate conversion (up-conversion)before inputting the resulting intermediate frequency signal into aconventional Costas loop arrangement. This is not the same as theapproach used by the provision of the receive modem analogue circuit224, which in contrast uses up-conversion as a fundamental elementplaying a feedback role within a new form of implementing a Costas looptype approach.

In other simpler embodiments, the discriminator and control functionmodule 512 may be omitted. However, in this embodiment, additionaladvantages are provided by the discriminator and control function module512 as follows.

In Costas loop type operation, the VCO can be difficult to implementbecause the Costas loop requires the offset being removed to be within acertain size, i.e. not too great. For example, if frequency differencesare too high at start-up, or phase rotation is too fast in the incomingsignal, there can be a failure to lock. This aspect is particularlyrelevant in the receive modem analogue circuit 224 as this has two VCOsoperating, and their relative differences of frequency play asignificant role. The discriminator module 514 monitors the residualfrequency difference at the output from the IQ demodulator 510 and usesthat measured residual frequency difference to control or specify thefrequency for the down-converter VCO 520, hence controlling orspecifying the relative frequency alignment between the two VCOs 520,522 at first lock-in attempts or at recalibration stages i.e. in effecteach time the Costas loop is being started up.

Note, in this embodiment the discriminator and control function module512 controls the relative frequency alignment between the two VCOs 520,522 by controlling (only) the down-converter VCO 520. However, this neednot be the case, and in other embodiments the discriminator and controlfunction module 512 may control the relative frequency alignment betweenthe two VCOs 520, 522 by controlling only the up-converter VCO 522 oreven by controlling both the VCOs 520, 522.

The discriminator module 514 and control function module 516 may beimplemented in any suitable manner to carry out the operations describedabove. Further details of the discriminator module 514 and controlfunction module 516 of this embodiment are as follows.

The discriminator module 514 operates on the baseband outputs 524 todetermine the value of any frequency offset that is caused in theseoutputs by the frequency difference between the two VCOs 520, 522. Oncethis value is known, it can be used via the control function module 516to adjust the down-converter VCO 520. In order to facilitate this, thebaseband inputs to the receive modem analogue circuit 224 are held atfixed levels, representing a fixed symbol. This is implemented bydisconnecting the baseband inputs 502 arriving from the transceiver 26and replacing them with a fixed level. Given that the symbol is nowunchanging, it is possible to implement the discriminator module simply;in this embodiment it comprises a complex baseband filter with aconstant frequency-amplitude slope so that the frequency can beascertained by comparing signal levels before and after the filter. Thisfrequency is in effect passed to the control function module 516. Thisimplementation of the discriminator module 514 is simple yet adequatesince it is only intended to measure and correct the frequency termswith sufficient accuracy that the Costas loop functionality can acquireonce the baseband inputs 502 arriving from the transceiver 26 are againapplied to the receive modem analogue circuit 224. In this embodimentthe Costas loop functionality can lock provided the residual frequencyerror is less than approximately 10 MHz.

Any appropriate Costas loop circuit may be used as the basis for theportion thereof employed in the Costas loop sub-module 518. For example,a Costas loop as described in “Synchronous data recovery in RFcommunication channels”; Song, B.-S.; IEEE Journal of Solid-StateCircuits, Volume: 22, Issue: 6, Digital Object Identifier:10.1109/JSSC.1987.1052870, Publication Year: 1987, Page(s): 1169-1176,the contents of which are incorporated herein by reference.

Any conventional implementation of a receive modem digital circuit maybe used for implementation of the receive modem digital circuit 222.Furthermore, it will tend to be the case that these can be simplifiedcompared to usual implementations due to the carrier recovery processand other processes already performed by the receive modem analoguecircuit 224. Indeed, a further advantage of the receive modem analoguecircuit 224 is that the carrier recovery process may be implemented moreeasily or more efficiently by the receive modem analogue circuit 224than would be the case for the digital recovery that would otherwiseneed to be implemented in the receive modem digital circuit 222. Infurther detail, the receive modem digital circuit 222 of this embodimentis arranged to perform (amongst possibly other functions) the following:clock recovery (i.e. recover the symbol clock from the data stream);recovery of frame-timing (i.e. determine where data frames start); andchannel coding (i.e. error correction).

For completeness, referring back to FIG. 2, it is noted that both thetransmit modem analogue circuit 124 and the transmit modem digitalcircuit 122 may be implemented in any conventional fashion.

Apparatus for implementing the above described circuits, including thereceive modem analogue circuit 224, may be provided by configuring oradapting any suitable electronic components or other apparatus, forexample one or more processors.

A relatively large number of communication units 6 may be provided, togive a corresponding number of bidirectional links with the productioncommunication unit 8, with these links operating simultaneously or inother overlapping temporal sense, whilst nevertheless using the samepair of transmit and receive frequencies, by providing a relativelynarrow antenna beam angle for the antennas 12, and positioning therespective communication units 6 so that their beams do not overlap whenthey are communicating with the production communication unit 8.Preferably the communication units 6 each have an antenna beam angle ofless than or equal to 2°. For example, in one embodiment, sixteenbidirectional links are provided by sixteen communication units whoseantennas each have a beam angle of approximately 1.2°, and the units arepositioned so that there is at least a 3° separation between eachbidirectional link's line of sight.

In any of the above embodiments, the transmission and reception RFfrequencies are preferably greater than or equal to 50 GHz, and yet morepreferable greater than or equal to 55 GHz.

In any of the above embodiments, a preferable frequency separationbetween receiving and transmitting on the bidirectional links is in therange of 4 GHz to 5 GHz. For example, in any of the above embodiments asuitable frequency pair may be one in which transmission by one or moreof the communication units 6 is performed at approximately 58 GHz andreception (by the same one or more communication units 6) atapproximately 62.5 GHz, or vice-versa (i.e. a frequency separationbetween transmit and receive of approximately 4.5 GHz).

In further embodiments, the communication units 6 are adapted to be usedin a reconfigurable sense, i.e. for use at other frequencies within agiven frequency band, for example at other frequencies within afrequency band of 56.5 GHz to 64 GHz (with change of diplexerfrequencies).

In the above embodiments, the communication system is used to providewireless links, e.g. fixed wireless links, as part of a televisionoutside broadcast arrangement. However, this need not be the case, andthe communication system or one or more of its elements may be used forother point-to-point applications where video data is to becommunicated, for example uncompressed high resolution video. Also, thevideo data formats and/or rates described in the above embodiments arenot essential, and other formats and/or rates may be communicated. Suchdata may be compressed or uncompressed as required. In yet furtherembodiments, data other than video data may be communicated, inparticular when the data flow rates are comparable to video data flowrate requirements.

In the above embodiments, the communication system is bidirectional.However, this need not be the case, and in other embodiments thecommunication system is unidirectional.

In the above embodiments the various components of the communicationunit are physically mounted in an enclosure, and the antenna isphysically mounted on the enclosure. However, these details need not bethe case. For example, in other embodiments the various components maybe mounted or otherwise contained in more than one enclosure, or may bemounted or otherwise arranged in an exposed manner not involving anenclosure as such. Also, the antenna may be located in a manner otherthan fixed on any enclosure, for example in the enclosure, or freestanding separate from the enclosure.

In the above embodiments, at least the majority of the circuitry for thetransmit and receive digital modem functions is provided on a respectivegiven single board, and at least a majority of the circuitry for thetransmit and receive analogue modem functions is provided on a furthergiven board. However, this need not be the case, and in otherembodiments these respective circuits may be provided on plural boards,and some or all the digital modem circuitry may be provided on a sameboard or boards as some or all of the analogue modem circuitry.

In the above embodiments, the diplexer 34 is formed from, and has theouter dimensions of, a rectangular shaped solid block or slab. In otherembodiments, the shape may be other than rectangular. Also, the blockneed not be formed from only a single block as such, for example twosub-parts could be adhered together. In the above embodiments thediplexer is made of aluminium finished with an Iridite (trademark)surface finish. However, these details are not essential, for example adifferent surface treatment, or no surface treatment, may be applied.Also, materials other than aluminium may be used for the diplexer, forexample brass or copper with silver plating to reduce millimeter wavelosses. In the above embodiments the laminated structure is provided bythe RF board 32 being bonded to a surface of the diplexer 34, however inother embodiments other fixing arrangements may be employed. In theabove embodiments the communication unit further comprises a separatepower supply board. However, this need not be the case, and in otherembodiments power supply components may be provided in-situ on the otherboards, or otherwise provided.

The relative arrangement, and stacking approach, in the aboveembodiments of the power supply board/digital modem (board)/analoguemodem (board)/transceiver is not essential, and these (or other elementsin other embodiments) may be physically arranged/stacked in other waysin other embodiments. The size of the enclosure described earlier aboveand indicated in FIG. 3 is merely exemplary.

Regarding the mounting arrangement of the transmit and receive ICs 50and 52, and other components, on the RF board 32, described above withreference to FIG. 4, the details thereof need not be as described in theabove embodiments. For example, in other embodiments, other ways ofmounting and connecting the transmitter IC 50 and the receiver IC 52 maybe employed. Also, the transmitter IC 50 and the receiver IC 52 need notbe positioned at positions that are approximately aligned with thepositions of the diplexer transmitter port waveguide opening 45 and thereceiver port waveguide opening 47 respectively, however this willincrease track lengths between the IC and the port coupling arrangement.

In other embodiments, different transmitter and receiver ICs to thoseused in the above embodiments may be employed instead.

The various details relating to the RF board, as described withreference to FIG. 5, are not essential, and in other embodiments otherforms and detail of RF board may be used instead.

Various details of the diplexer 34 waveguide structure and waveguideopenings, as described for example with reference to FIGS. 6A and 6B,are not essential, and in other embodiments other forms and detail ofwaveguide structure and waveguide openings may be used instead.

In the above embodiments the waveguide structure is formed in the solidblock of the diplexer by machining the solid block to hollow out thewaveguide structure. The machining is controlled, or further machiningis performed, to provide the filters. The waveguide filters provide lowinsertion loss and high Q factor so that the transmit and receivefrequencies can be placed closer together for a particular isolation.However, in other embodiments, other techniques may be used instead. Forexample, in other embodiments, a microstrip filter may be implemented onthe outer surface of the upper double-sided pcb 62. This would howeverhave higher insertion loss and lower Q factor.

Certain advantages that tend to be provided are as follows.

The above described use of a solid block diplexer with an RF boardbonded thereto provides a compact arrangement with advantageous balancebetween transmission and reception separation compared to dilution ofpower. This approach also advantageously allows the same polarisation tobe used for both transmission and reception (although this is notessential), which is particularly advantageous for outside broadcastapplications as this can accommodate to an extent the nature of theattenuation that is caused by rain, where vertical polarised signalssuffer lower rain attenuation compared to horizontally polarisedsignals.

The RF board 32 is relatively thin and requires mechanical support and aheat sink. Advantageously, the diplexer 34 can perform these functionsin addition to its fundamental diplexing role, thereby tending toprovide a compact and lightweight overall apparatus structure byavoiding or reducing the need for separate physical support and heatsink for the RF board.

A range of greater than 1 km based on use of QPSK modulation and forwarderror correction may be provided, despite operation being at a frequencyband located around 60 GHz.

A physically compact apparatus may be provided, despite operation beingat a frequency band located around 60 GHz.

Bi-directional duplex link operation using frequency divisionmultiplexing may be provided, despite operation being at a frequencyband located around 60 GHz.

The above potential advantages are particularly advantageous for use inoutside broadcast applications and the like.

In the above description, the various embodiments of analogue modemcircuits, and the various embodiments of carrier recovery methodsperformed by analogue modem circuits, have been described in relationto, and are particularly advantageous in the context of, the abovedescribed particular examples of wireless communication systems,wireless communication units, for example, ones including one or moreof: a block diplexer, bidirectional communication, differentialtransmission, single RF boards, single antenna, outside broadcast,point-to-point communication, bidirectional links, operation atfrequencies greater than 50 GHz, and so on. However, it will beappreciated that the described embodiments of analogue modem circuits,and the described embodiments of carrier recovery methods performed byanalogue modem circuits, represent embodiments of the present inventionin themselves and may be used in a large number of contexts andarrangements other than the ones described above.

The invention claimed is:
 1. An analogue modem circuit for use between aradio frequency receiver and a digital modem circuit, the analogue modemcircuit comprising: inputs for receiving a baseband RF input signal fromthe RF receiver; an up-converter with frequency supplied by anup-converter voltage controlled oscillator (VCO); a down-converter withfrequency supplied by a down-converter VCO; a Costas loop sub-module;and outputs for outputting baseband outputs from the down-converter tothe digital modem circuit; wherein: the up-converter is arranged to feedthe down-converter, and the Costas loop module is configured to performCostas loop functionality on the output of the down-converter to controlthe up-converter VCO frequency output to thereby control modification ofrotation of symbols of the baseband RF input signal as it isup-converted and then down-converted to provide the baseband outputs. 2.An analogue modem circuit according to claim 1, wherein at least one ofthe VCOs is configured to be controlled dependent upon a residualfrequency difference between the two VCOs at the output from thedown-converter, at a time when the Costas loop functionality is beingstarted.
 3. An analogue modem circuit according to claim 2, configuredso that the controlling will be performed at a first lock-in attempt ofthe Costas loop functionality.
 4. An analogue modem circuit according toclaim 2, configured so that the controlling will be performed at arecalibration stage of the Costas loop functionality.
 5. An analoguemodem circuit according to claim 2, configured so that the residualfrequency difference will be determined when holding the baseband inputsat fixed levels, representing a fixed symbol.
 6. An analogue modemcircuit according to claim 5, further comprising: a complex basebandfilter with a constant frequency-amplitude slope, wherein the residualfrequency is to be determined by comparing signal levels before andafter the filter.
 7. A carrier recovery method performed by an analoguemodem circuit for use between a radio frequency (RF) receiver and adigital modem circuit, the method comprising: receiving a baseband RFinput signal from the RF receiver at inputs of the analogue modemcircuit; supplying, via an up-converter voltage controlled oscillator(VCO), frequency to an up-converter; supplying, via a down-converterVCO, a frequency to a down-converter; feeding the down-converter fromthe up-converter; performing, via a Costas loop module, Costas loopfunctionality on an output of the down-converter to control theup-converter VCO frequency output to thereby control modification ofrotation of symbols of the baseband RF input signal as it isup-converted and then down-converted to provide baseband outputs; andoutputting, from the analogue modem circuit, the baseband outputs.
 8. Amethod according to claim 7, comprising: controlling at least one of theVCOs dependent upon a residual frequency difference between the two VCOsat the output from the down-converter, at a time when the Costas loopfunctionality is being started.
 9. A method according to claim 8,comprising: performing the controlling at a first lock-in attempt of theCostas loop functionality.
 10. A method according to claim 8,comprising: performing the controlling at a recalibration stage of theCostas loop functionality.
 11. A method according to claim 8,comprising: determining the residual frequency difference when holdingthe baseband inputs at fixed levels, representing a fixed symbol.
 12. Amethod according to claim 11, comprising: determining the residualfrequency difference by comparing signal levels before and after acomplex baseband filter.
 13. One or more processors arranged to operatein accordance with a carrier recovery method performed by an analoguemodem circuit for use between a radio frequency (RF) receiver and adigital modem circuit, the method comprising: receiving a baseband RFinput signal from the RF receiver at inputs of the analogue modemcircuit; supplying, via an up-converter voltage controlled oscillator(VCO), a frequency to an up-converter; supplying, via a down-converterVCO, a frequency to a down-converter; feeding the down-converter fromthe up-converter; performing, via a Costas loop module, Costas loopfunctionality on an output of the down-converter to control theup-converter VCO frequency output to thereby control modification ofrotation of symbols of the baseband RF input signal as it isup-converted and then down-converted to provide baseband outputs; andoutputting, from the analogue modem circuit, the baseband outputs.